It is known that, if exposed to an undesirable environment, the performance of a semiconductor opto-electronic device, such as a light-emissive diode, laser or photodetector can become degraded. Such degradation can occur even though sensitive surface areas of the device, particularly where an electric field is present during operation of the device in the vicinity of a p-n junction or a junction between semiconductor material and metal, are protected from the ambient by a deposited dielectric layer. For this reason a number of applications for semiconductor opto-electronic devices have required such devices to be hermetically packaged in order to reduce the risk of occurrence of this kind of performance degradation. The packaging must include provision, both for electrical connections with the device from outside the package, and for the feeding into the package, or out of it, of the optical signal that the device is designed to detect or produce. One way of effecting such provision is to provide a window in the package wall as for instance described in GB 2 208 944A in relation to a photodetector. If the photodetector is to receive light emitted from the end of an optical fibre, the construction of the package may be such as to make the minimum separation between the end of the fibre and the photodetector so great as to require some form of lens coupling between them. This may be provided by a lens within the package, by a lens outside the package, or by using a lens as part of the package window, as described in GB 2 208 944A. As an alternative to the use of a window, a wall of the package may be penetrated in a hermetically sealed manner by some form of light guide, as for instance described in GB 2 064 862A. In the case of the particular structure described in GB 2 064 862A, the outer end of the light guide is butted against the optical fibre, but a clearly valid alternative is to replace the light guide with an optical fibre having properties similar to, or identical with, those of the optical fibre whose output it is desired shall be detected by the photodetector.
The use of the optical fibre/guide hermetic feedthrough, by definition requires an hermetic seal around the optical fibre/guide, which is typically expensive to manufacture and difficult to test for leaks because the fibre is usually provided outside the enclosure with mechanical protection in the form of a plastics protective coating. The use of a window in place of the hermetic fibre-guide feedthrough avoids these particular problems, albeit at the expense of adding significantly to the complexity and expense of the provision of a mechanical link between the photodetector chip and the optical fibre whose output is to be detected by the chip.
The present invention is concerned with the provision of an alternative form of hermetic enclosure which does not involve any requirement for an optical fibre/guide hermetic feedthrough, and which affords the possibility of a relatively simple and cheap form of establishing mechanical coupling of the end of an optical fibre array so as direct light emitted therefrom on to the photosensitive areas of the photodetector.
The invention is not limited in its applicability solely to hermetically packaged photodetector arrays, but is applicable also to semiconductor opto-electronic device arrays that include of consist of elements that emit light, such as LEDs and VCSELs.
According to the present invention there is provided an opto-electronic device array assembly including a semiconductor chip having a monolithic array of planar construction semiconductor opto-electronic rear light entry/exit devices, which chip is bonded face down upon a ceramic substrate so as to constitute an hermetic enclosure with opposed walls constituted respectively by the chip and the ceramic substrate.